1. Technical Field of the Invention
The present invention relates to lead acid batteries for use as an electric source for automobiles and in other fields, and more particularly to a process for producing a grid for use in lead acid batteries.
2. Prior Art
Currently, there is an increasing tendency to use a lead-calcium alloy as the grid for lead acid batteries because of its excellent properties, i.e. a small loss in electrolytic solution after assemblage of battery and only a slight self-discharge during storage.
As compared with the lead-antimony alloy which has been used prior to lead-calcium alloy, however, the lead-calcium alloy is inferior in castability and mechanical strength after casting. For these reasons, it has hitherto been conventional to form a lead-calcium alloy into a grid by rolling its ingot into a sheet and then subjecting the sheet to an expanding treatment.
When an acid battery using a grid of lead-calcium alloy is left standing for a long period of time in a discharged state, a high resistance substance is formed at the interface between the positive electrode and the active material and this high resistance substance makes the next charging procedure impossible.
Accordingly, a first object of the present invention is to provide a process for producing a grid for use in lead acid batteries which solves the above-mentioned problem.
The second object of the present invention is to obtain a grid for use in lead acid batteries by a process which comprises superposing a sheet or a foil of a lead alloy on a sheet bar of a lead-calcium alloy, the lead alloy sheet or foil having a composition different from that of the sheet bar and having a thickness smaller than that of the sheet bar, followed by subjecting the superposed materials toa cold rolling to form an elementary sheet in which both the materials are integrated and then subjecting the elementary sheet to an expanding or punching process.
The third object of the present invention is to provide a grid for use in lead acid batteries which is easy to produce and low in cost.
Other objects of the present invention will become apparent from the examples of the invention described below.